JP2006221712A - Phase change type optical recording medium and recording method thereto, and evaluation method of transition linear speed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change type optical recording medium in which an amorphous mark can be exactly formed even on the condition that recording power is suppressed to some extent when high speed recording at DVD 8X is performed, and high modulation degree can be secured by regulating the range of reflectance change, and to provide a recording method to the recording medium and an evaluation method of transition linear speed of the recording medium. <P>SOLUTION: The phase change type optical recording medium is characterized in that when a transition linear speed Vt and the maximum recording linear speed V<SB>M</SB>have a relationship of Vt≤V<SB>M</SB>and when the minimum value of the ratio [R(v)/R<SB>1</SB>] of a reflectance R(v) obtained when a recording layer is irradiated with continuous light (DC light) having power Pi [mW] capable of heating the recording layer at its melting point or above at a linear speed v to a reflectance R<SB>1</SB>of a crystallin substance after initialization is defined as [R(v)/R<SB>1</SB>]<SB>min</SB>, the V<SB>M</SB>satisfies an expression [R(V<SB>M</SB>)/R<SB>1</SB>]<SB>min</SB>=0.60 to 0.85. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phase-change optical recording medium that records and reproduces information by causing optical changes in a recording layer material by irradiating a light beam, and is rewritable and compatible with high linear velocity recording. It is about.

DVD + RW, which is a rewritable phase change disk, is commercially available for 1 to 4 times speed. However, what is capable of further high-speed recording is desired.
For example, in Patent Document 1, the linear velocity range in which the reflectance starts to decrease due to continuous laser irradiation is a range of 8 m / s to 30 m / s, and the recordable linear velocity range is 1.2 m / s to 30 m / s. An optical recording medium that is less than or equal to s is disclosed, but the phase change recording layer has Sb and Te as essential elements, and in this composition, as will be described later, the phase change type light having the characteristics intended by the present invention is disclosed. A recording medium cannot be realized.
Further, in Patent Document 2, the linear velocity (reflectance lowering linear velocity) at which the reflectivity starts to decrease due to continuous irradiation of laser light having a power higher than the erasing power Pe at which optimum overwrite characteristics can be obtained on the low speed side is recorded. An optical recording medium characterized by being in a possible linear velocity range is disclosed, but there is no description that defines the amount of change in reflectance as in the present invention.

JP 2002-245663 A JP 2004-63002 A

The present invention is a rewritable DVD + RW phase change type that has the same capacity (4.7 GB) as a DVD-ROM and can perform recording even at a linear speed that is 8 times the reproduction speed of 3.49 m / s (hereinafter referred to as DVD 8 times speed). The purpose is to develop optical recording media. In order to develop a phase change type optical recording medium capable of 8 × DVD recording, it is necessary to make the erasing time faster than in the prior art. Therefore, it is necessary to greatly improve the crystallization speed of the recording layer. Since it is difficult to know the absolute value of the crystallization speed of the phase change recording layer, the transition linear velocity Vt is used as a substitute characteristic in the present invention. The transition linear velocity is defined as the linear velocity dependency R (v) of the reflectance obtained by irradiating the recording layer with continuous light (DC light) having an irradiation power Pi that can heat the recording layer to the melting point or higher. The linear velocity at which D (v) = − dR (v) / dv differentiated in (1) is maximized.
FIG. 1 shows the linear velocity dependency R (v) of reflectance when DC light is irradiated. FIG. 1 shows a case where the irradiation power Pi = 18 mW. R (v) / RI curve is obtained with the reflectance after initialization as RI, and R (v) is differentiated by the linear velocity v of the medium to obtain D (v) = − dR (v) / dv. The linear velocity when the differential coefficient becomes the maximum value is the transition linear velocity Vt. The transition linear velocity that can be read from this figure is approximately 23 m / s.

  When the transition linear velocity is relatively slow, a thick amorphous mark may be formed because the melted portion of the recording layer that has obtained heat by the condensed light is less likely to recrystallize due to the effect of residual heat. Easy. Recrystallization is a process in which a portion melted by irradiation with high power gradually returns to a crystalline state from its periphery when recording an amorphous mark. In fact, the 4X (DVD 4 × speed) DVD + RW disc currently on the market has a slow transition linear velocity of about 10 m / s, so if the recording power is set to about 16 mW, a high degree of modulation around 70% modulation can be secured. Can do. Here, the modulation degree is expressed as modulation degree = (Rtop−Rbot) / Rtop, where Rtop is the reflectance of the crystalline portion and Rbot is the reflectance of the amorphous portion. It means how much the difference in reflectance between the crystalline part and the amorphous part occupies the reflectance of the crystalline part.

  On the other hand, in developing a phase change optical recording medium capable of 8x DVD recording, the recording power of laser light is greatly increased when recording amorphous marks on the recording layer as the crystallization speed increases. The need to let it come out. When the crystallization speed is improved, recrystallization is facilitated and it is difficult to make the material amorphous. Therefore, a recording power is required to increase the cooling speed and provide a rapid cooling effect. DVD + RW and DVD-RW discs employ a multi-pulse recording method in which peak power Pp and bottom power Pb necessary for forming an amorphous mark are alternately repeated as a recording method for providing a rapid cooling effect. This is because the cooling effect is enhanced by increasing Pp and increasing the difference from Pb.

A relationship as shown in FIG. 2 can be predicted as a relationship between the recording speed of the phase change optical recording medium and the recording power at which the modulation factor characteristic is good. According to this figure, it is expected that a recording power exceeding 40 mW will be required in order to realize further high-speed recording of DVD 8 × speed or more. This suggests that as the recording scanning line speed increases, the amount of heat to be applied around the unit area also changes, so that a higher power is required as the recording power for forming the amorphous mark. However, since there is a limit to the improvement of the laser emission power, it is not preferable to increase the recording power every time just because of high-speed recording.
Further, in high-speed recording, when erasing information, it is necessary to quickly erase the amorphous mark, so it is necessary to increase the crystallization speed of the recording layer of the phase change optical disk. However, it has been found that if the crystallization speed is increased to some extent, the part once melted is easily recrystallized, and it becomes difficult to form an amorphous mark uniformly, so a high degree of modulation is ensured. It becomes difficult. Therefore, it is necessary to quickly erase the amorphous mark when erasing information, and to have a crystallization speed that does not cause much recrystallization of amorphous when information is recorded.

In summary, in a high-speed recording system, since the crystallization speed of the recording layer material must be increased, the amorphous mark is necessarily thinned by recrystallization, and the degree of modulation cannot be obtained. Accordingly, there is a possibility that ROM compatibility cannot be ensured unless the change in reflectance is included in the criterion.
Based on these problems, the present invention can accurately form amorphous marks even under conditions where the recording power is suppressed to some extent when performing high-speed recording at a DVD 8 × speed, and changes in reflectivity can be achieved. It is an object of the present invention to provide a phase change optical recording medium that can secure a high degree of modulation by defining a range, a recording method on the recording medium, and a method for evaluating a transition linear velocity of the recording medium.

The above problems are solved by the following first to seventh inventions (hereinafter referred to as the present inventions 1 to 7).
Linear velocity 1) and transition linear velocity Vt and the maximum recording linear velocity _{V M} is in the relationship of Vt ≦ _{V M,} and continuous light power Pi [mW] which can heat the recording layer above the melting point of the (DC light) The minimum value of the ratio “R (v) / R _I ” between the reflectance R (v) when irradiated at v and the crystalline reflectance R _I after initialization is [R (v) / R _I ] _min as, _{V M} is, _[R (V M) / _{R I] min} = from 0.60 to 0.85 phase-change optical recording medium which satisfies the.
2) The phase change optical recording medium according to 1), wherein 0.75 V _M <Vt ≦ V _M.
3) A lower protective layer having a thickness of 30 to 100 nm, a recording layer made of a phase change material having a thickness of 10 to 20 nm, an upper protective layer having a thickness of 3 to 15 nm, and a reflective layer having a thickness of 100 to 300 nm are formed on the substrate. The optical recording medium according to 1) or 2), wherein the optical recording media are laminated in order.
4) The phase change optical recording medium according to 3), wherein the phase change material contains at least four elements of Ga, Sb, Sn, and Ge.
5) The phase change according to 3) or 4), wherein the substrate has meandering grooves having a track pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.3 μm. Type optical recording medium.
6) Employing the EFM + modulation method, the pulse condition for recording the amorphous mark is 1 pulse when recording the 3T mark, and 1 when N increases by 2T when recording the (3 + N) T. 6. The recording method for a phase change optical recording medium according to any one of 1) to 5), wherein recording is performed using a recording strategy (2T periodic recording strategy) that adds a pulse.
7) changes due to Pi of the optical recording medium in a variety of linear velocity at the power Pi of the continuous light by irradiating each linear velocity R (v) / R _I a (Pi dependent) was measured, each linear velocity of based on this _[R (v) / R _I] was calculated _min, the value and practical maximum recording linear velocity _{V M} of the optical recording medium linear velocity in the range of 0.60 to 0.85, [R (V _M ) / R _I ] Select Pi that gives _min , and examine the linear velocity dependence R (v) of the reflectance obtained by irradiating the optical recording medium with the Pi, and use this to determine D (v) = The phase change light according to any one of 1) to 5), wherein -dR (v) / dv is obtained, and the linear velocity when the differential coefficient becomes the maximum value is set as the transition linear velocity Vt. Evaluation method of transition linear velocity Vt of recording medium.

Hereinafter, the present invention will be described in detail.
The above-mentioned transition linear velocity can be clearly understood as the change in reflectance becomes more conspicuous as the R (v) curve goes from low speed to high speed. For example, the graph shown in FIG. 3 represents the scanning line speed dependency R (v) / RI of the reflectance R when the continuous light irradiation power Pi = 12 to 18 [mW]. It can be seen that as the linear velocity of the optical recording medium increases from a low speed to a high speed, the reflectance starts to decrease at a certain value. On the low speed side, the phase change recording layer is once melted to the melting point or higher, and thereafter, the recording layer is crystallized to have a high reflectance. On the other hand, on the high-speed side, the phase change recording layer irradiated with continuous light of power Pi is once melted to the melting point or more, but the temperature rapidly decreases because the irradiation beam passes before crystallization, and as a result, The atomic structure in the molten state is formed and the amorphous state is formed, so that the reflectance is lowered.

Further, when the irradiation power Pi is less than a certain power, for example, Pi = 12 mW, the temperature does not rise to the melting point of the recording layer, and therefore the reflectance hardly decreases even if the speed is increased. When the irradiation power Pi is equal to or higher than a certain power, for example, when 13 mW ≦ Pi ≦ 18 mW, the temperature of the phase change material can be set to the melting point or higher, and the phase change material becomes a molten state. Then, the linear velocity v changes from a molten state to an amorphous state at a cooling rate of a certain level or more, and a decrease in reflectance can be measured. When the irradiation power Pi of the continuous light is increased to some extent, the degree of reflectivity reduction eventually begins to saturate. Therefore, in order to examine the reflectance change of the R (v) curve, the continuous light irradiation power Pi should be as strong as possible.
From this result, the transition linear velocity Vt can be obtained, but it can be said that if the recording is performed at a higher speed than Vt, the recording layer is easily made amorphous.
From the above, in a phase change optical recording medium capable of performing high-speed recording, it is possible to use an optical recording medium in order to accurately form an amorphous mark with a recording power as low as possible to ensure a high degree of modulation. maximum recording linear velocity as _{V M} a is preferably Vt ≦ _{V M.}

If the requirements defined in the first aspect of the present invention are satisfied, a phase-change optical recording medium in which the degree of modulation can be easily secured even at a linear speed corresponding to DVD 8 × speed can be obtained.
As you increase the irradiation power Pi of the continuous light, as shown in FIG. 3, consists of a certain linear velocity as R (v) / R _I is changed by Pi, the change begins to saturate Pi, i.e. R (V) There is Pi where / _RI does not change much. For example, fixed at a linear velocity v = 28 m / s, but was tried taking Pi on the horizontal axis is 4, the Pi is in the above 15mW are substantially constant _R (v) / R _I I understand. R _I represents the reflectance in the crystalline state obtained by initializing the recording layer in the as-deposited state immediately after film formation. Here, satisfactory while securing When _R (v) / R values of _{I [R} (v) / R _{I] min} when saturated at a certain Pi, a high degree of modulation at the maximum recording linear velocity _{V M} to obtain Do recording characteristics, _{V M} needs to satisfy the _[R (V M) / _{R I] min} = 0.60 to .85. If it exceeds 0.85, it becomes difficult to make it amorphous, and a high degree of modulation cannot be secured. On the other hand, if it is less than 0.60, the recording layer tends to become amorphous easily, and when information is erased, that is, when an amorphous part is erased, unerased residue is generated, resulting in poor recording characteristics. .

As defined in the present invention 2, in the case of 0.75V _{M <Vt} ≦ V M can obtain a high degree of modulation at the maximum recording linear velocity V _M, and it is possible to obtain good recording characteristics . When recording at a linear velocity v with respect to transition linear velocity Vt of the optical recording medium, if not satisfied Vt ≦ V _M, becomes liable melting recrystallization occurs because crystallization speed of the recording layer is faster Since the amorphous mark cannot be written thickly, it is difficult to ensure a high degree of modulation even with low power. For example, as shown in FIG. 5, when recording is performed at V _M = 28 m / s, in order to secure a modulation degree of 60%, a recording layer of Vt = 25 m / s may have approximately 29 mW, whereas Vt = 31 m. In the recording layer of / s, a recording power of about 36 mW is required. In either case, the recording characteristic (jitter) is less than 9%, which is good, but it can be seen that there is a large difference in the degree of modulation. When not satisfied 0.75 V M _<Vt, unerased even the jitter characteristic deteriorates to occur in an attempt to erase the information. Therefore, it is preferable that 0.75 V _M <Vt ≦ V _M is satisfied.

The present invention 3 defines a preferable layer structure of the phase change optical recording medium of the present invention.
The substrate is mainly made of plastic, but is not particularly limited as long as it has transparency and excellent planar accuracy. Conventionally, any optical recording medium conventionally used as a substrate can be selected and used. Typical examples of the substrate include a glass plate and a polycarbonate plate. Regarding the optical constant, the refractive index is preferably 1.5 to 1.6.
The lower protective layer formed on the substrate is preferably made of a material that is transparent, allows light to pass through, and has a melting point of 1000 ° C. or higher. Oxides, nitrides, sulfides and the like are mainly used, and among them, a mixture of ZnS and SiO ₂ is often used. In particular, ZnS: SiO ₂ = 80: 20 (molar ratio) is preferable. The film thickness is preferably in the range of 30 to 100 nm. If it is out of this range, it becomes difficult to ensure a favorable degree of modulation. Also, when the thickness is less than 30 nm, the reflectance variation with respect to the film thickness is large, so that it is difficult to produce stably. When the thickness is more than 100 nm, the film formation time becomes long and the productivity of the optical recording medium decreases.

The film thickness of the recording layer made of a phase change material formed on the lower protective layer is preferably in the range of 10 to 20 nm. If the thickness is less than 10 nm, a problem of deterioration due to repeated recording occurs. On the other hand, if it is thicker than 20 nm, the jitter characteristics deteriorate.
The upper protective layer laminated on the recording layer made of a phase change material is preferably a material having the same characteristics as the lower protective layer. The film thickness is desirably in the range of 3 to 15 nm. If the thickness is smaller than 3 nm, there arises a problem that the recording sensitivity is deteriorated or the modulation degree is lowered. On the other hand, if it is thicker than 15 nm, the recording mark is easily recrystallized due to the influence of residual heat generated during recording, and the recording characteristics are deteriorated.
Although a metal material is used as the reflective layer laminated on the upper protective layer, Al, Ag, Au, Cu and their alloy materials are often used from the viewpoint of optical characteristics and thermal conductivity. The film thickness is desirably in the range of 100 to 300 nm. If the thickness is less than 100 nm, the heat dissipation effect may not be obtained. On the other hand, if it is thicker than 300 nm, the heat dissipation effect does not change any more, and a film thickness that is not necessary is simply formed.

As the phase change material, a material containing at least four elements of Ga, Sb, Sn, and Ge as in the fourth aspect of the present invention is preferable.
The present invention aims at a phase change type optical recording medium capable of repetitive recording at a maximum recording speed of DVD 8 × speed. However, the phase change recording layer material of AgInSbTe type used for conventional DVD 1 to 4 × speed DVD + RW has a low crystallization speed and is not suitable for high-speed recording. Therefore, it is necessary to search for a phase change recording layer material that can be recorded even at a DVD 8 × speed. So far, three-element materials of Ga, Sb, and Sn and four-element materials of Ga, Sb, Sn, and Ge have been discovered, and high-speed recording can be achieved by changing the composition ratio of these constituent elements. It is possible to have a crystallization speed compatible with the above. Further, by recording each element within a range of several percent, a recording layer material capable of recording at DVD 8 times speed can be realized.

  In the fifth aspect of the present invention, a substrate having meandering grooves having a track pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.3 μm is used. The purpose of meandering the groove is to access a specific unrecorded track and to rotate the substrate at a constant linear velocity. In a DVD disc having a track pitch of 0.74 ± 0.03 μm, a push-pull signal is mainly extracted as a signal used to detect a tracking error. As for the push-pull signal, when the substrate is used at a laser wavelength of 660 nm used in DVD, the maximum signal intensity can be obtained when the groove depth is 55 nm. In order to adjust the reflectivity low and increase the amplitude of the push-pull signal, the groove depth should be deep, but in consideration of recording characteristics, it is preferably in the range of 22 to 40 nm. The groove width is preferably in the range of 0.2 to 0.3 μm in consideration of recording characteristics and signal characteristics.

The present invention 6 relates to a preferred recording method for the phase change optical recording medium of the present invention.
EFM + modulation system is adopted, and as a pulse condition for recording a mark, 1 pulse is added when recording a 3T mark, and 1 pulse is added every time N increases by 2 when recording (3 + N) T. Such a recording strategy (2T periodic recording strategy) is used. By providing irradiation pulses with a 2T cycle with respect to the recording clock, the modulation degree in high-speed recording can be greatly improved. A conventional 1- to 4-times speed DVD + RW optical disc employs a 1T period recording strategy. This is a recording method in which irradiation pulses are provided at a 1T period with respect to a recording clock. If this recording method is used for recording on a DVD 8 × speed phase change optical recording medium, the recording clock cycle is as short as 4.78 nsec, so that there is not enough cooling time between irradiation pulses, and the amorphous part is caused by the remaining heat of the next pulse. Will recrystallize, making it very difficult to form long amorphous marks. Therefore, the 1T period recording strategy is not preferable for high-speed recording of DVD 8 times.

The transition linear velocity Vt is evaluated by the method of the present invention 7.
To evaluate Vt, first determines practical maximum recording linear velocity V _M of the optical recording medium. The determination method will be described with reference to FIG. FIG. 6 shows changes in R (v) / RI of each linear velocity due to Pi when the optical recording medium is irradiated with continuous light with an irradiation power Pi at linear velocity v = 21, 28, 35 m / s. Sex). As can be seen from the figure, at v = 21 m / s, the crystallization speed of this optical recording medium is fast, so that the recording material cannot be sufficiently melted even when irradiated with any Pi, and amorphization does not occur. There is no decrease in reflectivity. In this case, _[R (21) / R _I] min is about 0.98, 21m / s is not a practical maximum recording linear velocity _{V M} of the optical recording medium. In v = 28m / s, saturated As you increase the irradiation power Pi begins to decrease gradually _R (v) / R _I, eventually R (28) from Pi = 16 mW / _{R I} is [R (28) / R _I ] min = 0.68 is obtained. Therefore 28m / s it can be said to be appropriate _{V M.} In addition v = 35m / s, when is increased irradiation power Pi gradually _R (v) / R _I begins to decrease. Can not know the saturation value in the range of Pi in figure, _[R (35) / R _I] because min is obvious that less than 0.6 35m / s is inappropriate as _{V M.} Therefore, when Pi (= 16 mW) giving [R (28) / R _I ] min is selected from the result of Pi dependence of R (28) / R _I at v = 28 m / s, the transition linear velocity Vt is evaluated. I know good things.
Next, the linear velocity dependency R (v) of the reflectance obtained by irradiating the optical recording medium with continuous light (DC light) having an irradiation power Pi (16 mW) was examined, and D (v) = − dR (v ) / Dv, and the linear velocity at which the differential coefficient is the maximum value is defined as the transition linear velocity Vt.

  According to the present invention, when performing high-speed recording at a DVD 8 × speed, an amorphous mark can be accurately formed even under conditions where the recording power is suppressed to some extent, and the range of reflectance change is defined. It is possible to provide a phase change optical recording medium capable of ensuring a high degree of modulation, a recording method on the recording medium, and a method for evaluating a transition linear velocity of the recording medium.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.
The phase change optical discs produced in the examples and comparative examples have at least a lower protective layer, a phase change recording layer, an upper first protective layer, and an upper second protective layer on a polycarbonate substrate for DVD + RW transferred with a spiral continuous groove. The reflective layers are laminated in this order.
The phase change optical disks used in the examples and comparative examples have a lower protective layer made of ZnS-SiO ₂ having a thickness of 58 nm and an interface layer made of SiO ₂ having a thickness of 2 nm on a transparent substrate, GaSbSnGe or GaSbSnGeIn (each example and The composition ratio of the comparative example is as shown in Tables 1 and 2). The phase change recording layer is 16 nm thick, the upper first protective layer made of ZnS—SiO _{2 is} 7 nm thick, and the upper second protective layer is made of TiC—TiO. The thickness is 4 nm, and the reflective layer made of Ag is 140 nm thick. As the film forming apparatus, an 8-channel sputtering apparatus manufactured by Balzers was used.
The completed disc was initialized with a phase change optical disc initialization device to obtain a DVD + RW disc. Initialization uses an optical head with a focused beam diameter of 75 μm, power 1800 mW (here, LD power consumption, different from irradiation power), scanning speed 20 m / s, feed 50 μm / rotation. This was done by crystallization.
Information is recorded on the phase change recording layer by forming a peak power Pp for forming a recording mark by forming an amorphous state, a bottom power Pb for facilitating the formation of an amorphous mark by applying a quenching effect, and forming a crystalline material. This was performed using a 2T periodic recording strategy that was intensity-modulated with three levels of erasing power Pe (Pp>Pe> Pb) for erasing information. The strategy pulse generator is DTG-5274 manufactured by Nippon Tektronix Co., Ltd., and the setting resolution is 0.026159 × 16 × v [GHz] when the recording scanning speed is v times the speed of DVD (v ≦ 8). The evaluation apparatus used is DDU-1000 manufactured by Pulse Tech Co., Ltd., with NA = 0.65 of the objective lens and laser wavelength λ = 660 nm used for recording / reproduction. The recording power spec is 40 mW at maximum for Pp and 18 mW for Pe. Since Pb has a power as small as possible to give a rapid cooling effect, recording was carried out with a fixed value of 0.1 mW. The degree of modulation and jitter were measured by recording 10 times of overwrite on 3 tracks and measuring the reproduction signal of the middle track. The higher the degree of modulation, the better. The DC (Data to Clock) jitter represents the time lag between the edge of the amorphous mark and the rising edge of the clock cycle Tw, and a smaller value is better.

Examples 1-20, Comparative Examples 1-23
Disks of Examples 1 to 20 and Comparative Examples 1 to 23 were prepared using recording layer materials having the compositions shown in Table 1. Table 1 summarizes the transition linear velocity Vt (m / s), the value of [R (28) / R _I ] min, the degree of modulation (Mod [%]), and DC jitter when recording at Pp = 32 mW. Showed. Vt was measured at Pi = 16 mW. The linear speed of 28 m / s is a DVD 8 × speed. The modulation factor and DC jitter are data when overwriting is performed 10 times. A mark with a modulation degree of 60% or more was marked with ◯, and a mark with less than 60% was marked with a cross. Further, ○ is given to those having a jitter characteristic of less than 9%, and × to 9% or more.
The disks of Examples 1 to 20 satisfy the requirements of the present invention 1, and have good modulation and good jitter characteristics when recorded at a linear velocity of 28 m / s. Further, the transition linear velocity Vt satisfies the requirement of the present invention 2, and corresponds to a range satisfying the requirement of the present invention 1. On the other hand, since Comparative Examples 1 to 23 do not satisfy the requirements of the present invention 1, when recording at a linear velocity of 28 m / s, a modulation degree of 60% or more cannot be secured.
FIG. 7 is a graph of the data in Table 1. [R (28) / R _I ] min of each disk is plotted on the horizontal axis, and the degree of modulation is recorded on the vertical axis when recording is performed by the EFM + modulation method using the 2T periodic recording strategy. From this figure, it can be seen that the condition for satisfying the modulation degree of 60% or more is [R (28) / R _I ] min ≦ 0.85. Further, it can be seen that the condition for satisfying the jitter characteristic of less than 9% which is the DVD standard value is [R (28) / R _I ] min ≧ 0.60. The reflectance at the same linear velocity as the recording linear velocity R (V) is too lowered relative to R _I, can not be completely erased amorphous marks for crystallization speed of the recording layer is too slow, it can not be completely crystallized It is considered that the jitter is deteriorated due to the above.

Examples 21-25, Comparative Examples 24-28
The main object of the present invention is to provide a phase change type optical recording medium capable of recording in high-speed recording at 8 × DVD, but the medium of the present invention can be recorded even at a linear velocity lower than DVD 8 ×. Indicates. Here, an example of DVD 5 × speed (17.5 m / s) is given.
Disks of Examples 21 to 25 and Comparative Examples 24 to 28 were prepared using recording layer materials having the compositions shown in Table 2. Table 2 summarizes the transition linear velocity Vt (m / s), the value of [R (17.5) / R _I ] min, the modulation degree (Mod [%]) at Pp = 32 mW, and the DC jitter of each disk. Indicated. The evaluation contents and evaluation criteria of the modulation degree and DC jitter are the same as those in Table 1.
Examples 21 to 25 satisfy the requirements of the present invention 1, have a good degree of modulation when recorded at a linear velocity of 17.5 m / s, and good jitter characteristics. Further, the transition linear velocity Vt satisfies the requirement of the present invention 2, and corresponds to a range satisfying the requirement of the present invention 1. On the other hand, Comparative Examples 24-28 do not satisfy the requirements of the first aspect of the present invention, and therefore, when the recording is performed at a linear velocity of 17.5 m / s, a modulation degree of 60% or more cannot be secured.

The figure which shows the linear velocity dependence R (v) of the reflectance after DC light irradiation, and a differential coefficient. The figure which predicted the relationship between recording power and recording speed. The figure which shows the linear velocity dependence of R (v) / RI. The figure which shows the Pi dependence of R (28) / RI. The figure which shows the modulation degree difference by the difference in Vt in recording speed 28m / s. The figure which shows the change (Pi dependence) of R (v) / RI of each linear velocity by Pi when the optical recording medium is irradiated with continuous light with power Pi at linear velocity v = 21, 28, 35 m / s. . The figure which made the data of Table 1 into a graph.

Claims (7)

Transition linear velocity Vt and the maximum recording linear velocity _{V M} is, Vt ≦ _V have a relationship of _M, and the linear velocity v of the continuous light (DC light) irradiation power Pi that can heat the recording layer above the melting point [mW] [R (v) / R _I ] _min is the minimum value of the ratio “R (v) / R _I ” of the reflectance R (v) when irradiated with the above and the crystalline reflectance R _I after initialization. , V _M satisfies [R (V _M ) / R _I ] _min = 0.60 to 0.85. 2. The phase change optical recording medium according to claim 1, wherein 0.75 V _M <Vt ≦ V _M.   On the substrate, a lower protective layer having a thickness of 30 to 100 nm, a recording layer made of a phase change material having a thickness of 10 to 20 nm, an upper protective layer having a thickness of 3 to 15 nm, and a reflective layer having a thickness of 100 to 300 nm are arranged in this order. The optical recording medium according to claim 1, wherein the optical recording medium is laminated.   4. The phase change optical recording medium according to claim 3, wherein the phase change material contains at least four elements of Ga, Sb, Sn, and Ge.   5. The phase change light according to claim 3, wherein the substrate has meandering grooves having a track pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.3 μm. recoding media.   EFM + modulation system is adopted, and the pulse condition for recording the amorphous mark is 1 pulse when recording a 3T mark, and 1 pulse every time N increases by 2T when recording (3 + N) T. 6. The recording method for a phase change optical recording medium according to claim 1, wherein recording is performed using a recording strategy (2T periodic recording strategy) to be added. Changes due Pi of the optical recording medium various irradiated with continuous light of linear velocity by a power Pi in each linear velocity of the R (v) / to R _I to (Pi-dependent) was measured, each linear velocity of based on this [R (v) / _{R I]} was calculated _min, the value and practical maximum recording linear velocity _{V M} of the optical recording medium linear velocity in the range of 0.60 to 0.85, [R _(V M) / R _I ] The Pi that gives _min is selected, the linear velocity dependency R (v) of the reflectance obtained by irradiating the optical recording medium with the Pi is examined, and this is used to obtain D (v) = − dR. 6. The phase change optical recording medium according to claim 1, wherein (v) / dv is obtained, and the linear velocity at which the differential coefficient becomes the maximum value is the transition linear velocity Vt. Evaluation method of transition linear velocity Vt.

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